Varietal differences of dose response rice allelopathy on annual ryegrass

Weeds are continuing a constant problem in Australian cropping system. Annual ryegrass (Lolium rigidum) is a ubiquitous weed of southern Australia, infesting the majority of crops. The prospects of herbicide resistance necessitate considering alternative options such as the allelopathic potential of crops for weed suppression. To assess the dose response allelopathic prospects of rice, a laboratory-based root exudates bioassay was conducted using ECAM (Equal-Compartment-Agar Method). The allelopathic effects of two different genotypes (Quest and M 205) and five different densities (0, 5, 10, 15 and 20 seeds/beaker) of rice against annual ryegrass were investigated. During harvest the inhibited root, and shoot length was measured, the tissue structure of ryegrass root was also observed under electronic microscope. The experiment was designed as a randomized complete block with three replications and conducted under control conditions. Results showed that rice root exudates reduced the seedling growth of ryegrass with increasing density and genotype. Quest showed strong allelopathic potentiality than M 205 against ryegrass. The root growth of ryegrass was most infected than shoot by rice root exudates. The cellular study also suggests high density of rice increase high amount of allelochemicals in agar medium that caused damage of ryegrass root tissue system. These investigations also suggest that there are opportunities to explore dose response (hormesis) allelopathic effect of rice genotypes to control ryegrass.